This invention relates generally to the field of towing and more specifically to an operating system for towed vehicle electric brakes.
This invention represents an improved method of controlling electrically operated towed vehicle brakes. Electric towed vehicle brakes have been used for many years when medium sized vehicles are towed with light to medium duty vehicles such as light trucks and motor homes. Typically the tow vehicle is equipped with an electric towed vehicle brake controller that is mounted in the passenger compartment within sight and reach of the driver. The concept of the electric towed vehicle brake controller is to provide an electric signal that actuates the towed vehicle brakes causing them to create a retarding force that works in unison with the brake system of the towing vehicle. Currently marketed brake controllers can be grouped into one of three methods of operation; time based, acceleration based, or hydraulic pressure based. Time based units are the simplest. Upon initiation of braking, these units create a periodic increasing brake control signal which rises to a maximum level. The rate of signal increase and maximum signal level are set by the user prior to braking initiation. Acceleration based units create a brake control signal that is proportional to the deceleration rate of the tow vehicle—towed vehicle combination. Typically these units have user-set parameters for the orientation of the acceleration sensing device and the maximum signal level. The maximum signal level parameter also controls the proportionality constant of the controller output. Hydraulic pressure based units sense the hydraulic pressure in the brake system of the tow vehicle and create a brake control signal that is proportional to this pressure. These units usually have a user-set parameter of the maximum signal level which also controls the proportionality constant of the controller output.
Some have attempted to use the longitudinal force between the tow vehicle and towed vehicle to control electric towed vehicle brakes. These prior attempts have created a brake control signal that had a linear relationship to the longitudinal force. Because electric brake torque is not a linear function of applied power, the response of these systems can create undesirable tow vehicle-towed vehicle brake balance. Additionally, these units could not produce any brake control signal if the towed vehicle was not connected to the longitudinal force sensing hitch mechanism. Currently, several general hitch configurations are available such as fifthwheel, gooseneck, receiver type, and bumper/drawbar configurations. A towed vehicle connected to a hitch configuration that did not contain a longitudinal force sensor would not receive a brake control signal.
All currently marketed electric brake controllers require the user to set parameters for proper operation. For optimum tow vehicle-towed vehicle combined brake performance, these parameters need to be changed when towing conditions change, such as; changing to a different towed vehicle, a change in towed vehicle load, a change in general driving speeds, a change in towed vehicle brake temperatures or when the towed vehicle brakes become wet, and many other changes in towing conditions. Thus it is difficult to get and keep current brake controllers properly adjusted. All current brake controllers provide instructions to assist the user in setting the various parameters. However, this process can be difficult, time consuming, and involves putting the tow vehicle-towed vehicle combination into motion. All of these issues represent potential safety hazards. Driving a tow vehicle-towed vehicle combination with an electric brake controller that is not adjusted to optimum settings increases stopping distances and can put excessive energy into one of the vehicle service brake systems.
Time based brake controllers require two user set parameters. The maximum signal level parameter functions as the proportionality constant between the tow vehicle and the towed vehicle brake characteristics. The rate of increase parameter represents a very simplistic method of brake modulation. Because these parameters are set prior to the initiation of the braking event, these brake controllers do not react to differences in braking demand from one braking event to the next, or within a single braking event.
Without user intervention, these controllers create the same response even though one braking event may be a panic brake to avoid an obstacle in the road and the next braking event may only require a slight reduction in speed. The parameters dictate the progress of the braking event. Some users attempt to change these parameters during the braking event, this is a safety hazard as it detracts the driver's attention from operating the tow vehicle.
Acceleration based controllers also require two user set parameters. The maximum signal level parameter functions as the proportionality constant between the tow vehicle and the towed vehicle brake characteristics. The acceleration sensor orientation adjustment changes the relationship between the sensed vehicle acceleration and gravity. This process attempts to create a favorable modulation of the towed vehicle brake effort. Because the tow vehicle—towed vehicle unit is essentially rigidly coupled in a longitudinal sense, both tow vehicle braking effort and towed vehicle braking effort affect sensed longitudinal acceleration. These controllers cannot determine the relative contribution of the towed vehicle brakes to the combined vehicle braking effort. Thus modulation is a delicate balance that is difficult to maintain when the tow vehicle orientation relative to gravity changes or other towing conditions change.
Hydraulic pressure based controllers require the user to set the maximum signal level. The maximum signal level parameter functions as the proportionality constant between the tow vehicle and the towed vehicle brake characteristics. The control of the towed vehicle brake modulation is based on the tow vehicle hydraulic fluid pressure. Changes in tow vehicle brake temperature and surface friction conditions (example, wet brake surfaces) require a change to the proportionality constant to maintain balance between tow vehicle and towed vehicle brake efforts. Also a change in the towed vehicle brake characteristics (such as changing towed vehicles, changing towed vehicle load, etc.) requires a change in the proportionality constant. Additionally, the installation of these types of controllers requires modification of the tow vehicle hydraulic brake system. This is undesirable from a time and liability standpoint.